Monica Lewinsky finally had her moment of revenge yesterday when she gave evidence against her former friend Linda Tripp, who is on trial for illegally taping their telephone conversations about her affair with Bill Clinton.

The former White House intern told prosecutors at a court in Ellicott City, Maryland, how frightened she had been when she saw accounts of her private exchanges with Ms Tripp printed in Newsweek. She was giving evidence at a hearing to determine what evidence the prosecution can use in a trial due to start on January 18.

"It terrified me," she said. "I was concerned about the privacy of my relationship being revealed."

Ms Lewinsky's testimony was vital in determining Ms Tripp's fate, because she said she had not given her friend consent for the taping and because of her first-hand recollection of their phone conversations.

Ms Tripp is facing two charges: illegally recording Ms Lewinsky and providing the tape to Newsweek. Each charge carries a maximum of five years in prison and a $10,000 (£6,250) fine.

The case against Ms Tripp cannot be based, even indirectly, on information she provided to Kenneth Starr, the independent counsel who was investigating the president, in return for immunity for prosecution.

Although Ms Tripp, a former White House secretary, made more than 20 hours of tapes of her rambling dialogues with Ms Lewinsky, the charges against her refer only to a tape made on December 22 1997 - before her immunity was approved by a court - which Newsweek journalists were allowed to hear. Ms Lewinsky testified that she remembered the conversations which appeared in Newsweek without having to refer to Ms Tripp's later testimony in the Starr report.

Ms Lewinsky's sense of betrayal was one of the personal dramas at the heart of the impeachment crisis. Asked for a final statement at the end of her grand jury testimony last year, she declared: "I hate Linda Tripp."

The two are likely to meet face to face if the case goes to trial next year.

As the prosecution has gathered its evidence in the pre-trial hearings, it has become clear that Ms Tripp's love of gossip has been her own worst enemy.

Friends from her Maryland bridge club testified that she had chatted constantly about her intimate conversations with a presidential girlfriend and her recordings of those chats. Ms Tripp's bridge partners said they had known about the tape recorder in the autumn of 1997, long before the Starr report emerged.